The candidate plans to remain at the University of Alaska to pursue research on his unique animal model, the hibernating arctic ground squirrel Spermophilus parryii. The award would enable him to increase his time available for research from approximately 65 to 85%. Because the investigation of freeze resistance involves techniques and approaches in which the candidate has not been specifically trained, receipt of an RCDA would be especially advantageous in allowing him time to interact with experts in cryobiology at other institutions. The Institute of Arctic Biology fully supports the candidate's work and offers a uniquely appropriate situation for the studies in terms of environment and facilities; the relative geographical isolation and small size of the Institute, however, limit the potential for interactions unless travel is made possible by limiting non-research responsibilities. The proposed research investigates (I) interrelationships between the reproductive endocrine system and control over seasonally changing body temperatures (Tb's) in hibernating mammals, and (II) mechanisms by which S. parryii can adopt subzero Tb's without freezing. Aims related to reproductive function and hibernation include: (1) measuring plasma reproductive hormone levels at the end of hibernation; (2) testing for CNS sensitivity to androgen inhibition of hibernation; nd (3) determining if plasma steroid hormone-binding proteins prevent such inhibition during hibernation. Aims related to freeze resistance include: (1) determining limits to subzero tolerance and testing blood from freeze-resisting animals for antifreeze and cryoprotectants; (2) measuring seasonal changes in blood supercooling points and serum proteins and lipoproteins; (3) identifying ice nucleation factors in blood and determining if ground squirrels eliminate these to avoid freezing; (4) artificially inoculating freezing in supercooled animals to investigate mechanisms of freeze defense; and (5) examining the role of nonshivering thermogenesis in stabilizing subzero hypothermia. These experiments should elucidate novel functional relationships between the reproductive endocrine system and CNS control over Tb. They address the question of how reproductive recrudescence begins during the constant darkness and periodic low body temperatures of hibernation. Other experiments investigate basic questions about apparently unique mechanisms of freeze resistance in mammals, answers to which may relate to cryopreservation of transplant organs and tolerance to severe hypothermia.